Although the demand for A319 alloy has increased in recent years, thermal fatigue resistance of the alloy is still one of the most important challenges in engine applications, especially in the newer generation of engines in which cylinder spacing has been reduced. According to the previous studies there are several parameters that improve thermal fatigue resistance such as: low SDAS, fine grain size, low porosity level, and low intermetallic content.
Cooling rate has a direct effect on the shape, size, and distribution of the microstructural phases, as well as on the scale of the dendrites, and pore size. High cooling rates can improve thermal fatigue resistance, as a result of fine microstructure and small pore size. On the other hand, thin sections of a mold may not properly fill and “Cold Shuts” may result, if high cooling rates are applied.
One approach to balance these phenomena is to use a water-cooled chill where water cooling is activated part way through the casting sequence. This type of chill causes a lower cooling rate initially, when the filling procedure is occurring, and after filling, the cooling rate increases to reduce the microstructure size. The results show that this method has the potential to both avoid cold shuts and miss-runs and improve the cast microstructure farther into castings remote from the chill.
A mathematical model has been developed in “ANSYS CFX 12.0” to evaluate the effectiveness of this concept quantitatively. The model simulates the behavior of the Casting/chill interface and also predicts the cooling rates resulting from different casting conditions when using solid chill and water-cooled chill.

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